1. Field of the Invention
This invention relates to front wheel suspension systems for motorcycles and, more particularly, to a front wheel suspension system of a linkage type.
2. Description of Relevant Art
There are generally known motorcycles which have a front wheel suspension including an upper fork rotatably mounted on a head pipe secured to the front end of a frame and a lower fork supporting the front wheel and directly or indirectly coupled to a lower portion of the upper fork so that vertical displacement of the front wheel following irregular road surfaces is allowed by up-and-down swinging movement of the lower fork.
In the motorcycle having such front wheel suspension system, a cylinder type damper is provided between the upper and lower forks, and the up-and-down displacement of the front wheel is damped by damping force provided by the cylinder type damper which is elongated and contracted with the swinging of the lower fork. With the front wheel suspension system of this construction, the cylinder type damper should at least have a length corresponding to the swing stroke of the lower fork. That is, the length of the damper has to be set according to the swing stroke. In addition, substantially one half of the weight of the damper acts upon the front wheel and lower fork. Therefore, it is difficult to reduce the so-called "unsprung weight", the reduction of which is effective for improving followability characteristics and comfort. In a further aspect, oil seal members in the cylinder type damper must be pressure-bearing seal members so that they can provide seals with respect to operating fluid which is pressurized to a high pressure inside the damper when damping force is generated. Therefore, the seal force of the pressure-bearing seal members constitutes a resistance against the operation of the damper as it is elongated or contracted, thus adversely affecting the damping force characteristics.